Glucose uptake and release by mammalian cells is a tightly controlled process, mediated by a family of intrinsic membrane proteins (facilitative glucose transporters) and subjected to hormonal and metabolic regulation, whose dysfunction may produce insulin-resistance seen in diabetes and obesity. The long term goal of this proposal is to identify the nature of the transporter defects underlying these diseases. More immediate goals are to determine the detailed protein structure to understand how it translocates glucose and how it is regulated by metabolites and hormones. Specifically, we propose and will test a discrete molecular model for the transmembrane helices (TMHs) structure of GLUT1, a member of this protein family. We will identify those TMH amino acid residues (i) that line putative glucose channel by covalently labeling them with transportable glucose analogs, (ii) that involved in transmembrane helix packing by chemical crosslinking and by site-directed pyrene labeling of paired Cys replacement mutants, and (iii) that interface with the lipid bilayer using lipophilic probes. We will also try to grow protein crystals suitable for X-ray and/or electron diffraction studies.